[LeetCode] Subsets 解题报告

Given a set of distinct integers,  S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If  S =  [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

» Solve this problem

[解题思路]
这个就是排列组合中的排列问题。递归如下逻辑：
Func Generate
对于输入字符串s的每一位字符
        选取该字符到子集合中，并输出
        如果，当前字符不是最后一位字符
                 递归调用Generate,处理下一位字符

[Code]

1:    vector<vector<int> > subsets(vector<int> &S) {  
2:      // Start typing your C/C++ solution below  
3:      // DO NOT write int main() function  
4:      vector<vector<int> > result;  
5:      vector<int> output;      
6:      if(S.size() ==0) return result;  
7:      result.push_back(output);  
8:      sort(S.begin(), S.end());  
9:      generateSub(S, 0, result, output);  
10:    }  
11:    void generateSub(  
12:      vector<int> &s,   
13:      int step,   
14:      vector<vector<int> > &result,  
15:      vector<int>& output)  
16:    {  
17:      for(int i = step;i<s.size(); i++ )  
18:      {  
19:        output.push_back(s[i]);  
20:        result.push_back(output);  
21:        if(i< s.size()-1)  
22:          generateSub(s, i+1, result, output);  
23:        output.pop_back();  
24:      }  
25:    }